JPH02284630A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a catalyst due to the formation of salt by passing exhaust gas and ammonia through the catalyst supported on a heating element and heated by heat from the element and reducing and decomposing NOx in the exhaust gas during passing. CONSTITUTION:Exhaust gas contg. NOx and ammonia are passed through a catalyst (e.g. V2O3) supported on a heating element 2 and heated by heat from the element 2 and the NOx is reduced and decomposed during passing. Since the NOx reacts rapidly with the ammonia on the surface of the catalyst, salt lowering the catalytic performance is not formed even in the case of exhaust gas at low temp., the deterioration of the catalyst can be prevented and the cost required to raise the temp. of gas is made unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an exhaust gas treatment method for removing nitrogen oxides from exhaust gas generated from garbage incinerators, sintering furnaces, coke ovens, nitric acid plants, and the like.

<Problems to be Solved by the Prior Art and the Invention> In order to prevent air pollution, it is required to remove nitrogen oxides contained in exhaust gas discharged from garbage incinerators and the like. As a method for removing nitrogen oxides, a method of reducing and decomposing nitrogen oxides into nitrogen and water using ammonia as a reducing agent is generally adopted.

However, when the exhaust gas is a low-temperature exhaust gas with a temperature of 300° C. or less, there are the following problems.

(1) Ammonia used as a reducing agent is nitrogen oxide No.
This reaction produces salts such as NH4NO2 and NH4NO3, which clog the pores of the catalyst and cause a decline in catalyst performance. This problem occurs when the exhaust gas temperature is 150℃.
It is noticeable in the following cases.

In addition, if the exhaust gas contains sulfur oxides,
This reacts with ammonia to produce salts such as NH4HSO3 and (NHa)2SO4, causing the same problem as above.

(In the reduction process of 2-nitrogen oxides, the following steps occur: gas diffusion into the catalyst layer, diffusion within the catalyst layer, and then a reduction reaction. Of these, the reduction reaction is the rate-limiting step, and the reaction rate is extremely slow. There was a problem.

(3) In order to solve these problems, it is possible to raise the exhaust gas temperature, but this is not practical because the cost of raising the temperature increases.

Incidentally, Table 1 shows the concentrations of nitrogen oxides and sulfur oxides in the exhaust gas discharged from each exhaust gas source and the exhaust gas temperature. However, these numerical values show an example.

Table 1 Since most of the nitrogen oxide-containing exhaust gases are low-temperature exhaust gases of 300° C. or lower, there is a strong demand for a solution to the above-mentioned problems.

The present invention has been made in view of the above circumstances, and is capable of reductively decomposing nitrogen oxides at a high reaction rate without causing deterioration of catalyst performance even with low-temperature exhaust gas, and in addition, is a low-cost exhaust gas. The purpose is to provide a processing method.

<Means for Solving the Problems> The exhaust gas treatment method of the present invention passes exhaust gas containing nitrogen oxides and ammonia through a catalyst supported on a heating element and heated by heat from the heating element. It reductively decomposes the nitrogen oxides inside.

In other words, the present invention makes it possible to highly efficiently reductively decompose nitrogen oxides with ammonia on the catalyst surface by increasing the catalyst temperature even with low-temperature exhaust gas.
As a result, deterioration of the catalyst due to salt formation is prevented, and the process can be performed at lower cost than when the gas temperature is raised.

In the present invention, examples of the heating element used include a heating resistor made of a thin wire mesh, metal plate, etc. having a large number of pores, and generating heat when energized. The wire mesh can be made from metal wire. Further, the pores in the metal plate can be formed, for example, by etching, punching with a mold, or lath processing.

Examples of metal materials used include simple metals such as iron, cobalt, molybdenum, titanium, zirconium, chromium, silver, gold, copper, nickel, and tin, and various iron alloys including stainless steel (such as 5US430.5US304). ,
Examples include alloys such as copper alloys, nickel alloys, tin alloys, and chromium alloys.

The diameter of the pores is 30 μm or more, more preferably 200 to 50 μm.
The thickness is preferably 0 μm from the viewpoint of reactivity and pressure loss. When the diameter of the pores is smaller than 30 μm, the reactivity increases, but pressure loss also increases, which is not preferable. On the other hand, if the diameter is excessively large, there will be no pressure loss, but
Reactivity tends to decrease.

Furthermore, the heating element material in the present invention is not limited to the above-mentioned heating resistor, but may include, for example, the above-mentioned wire mesh or metal plate made of a material having high thermal conductivity (such as aluminum). Similar effects can also be obtained when heat is supplied from another heat source to generate heat.

For example, V203, WO3, M
o53, Cr2 03 Fe2 03
, CO304, MnO2, N iO, etc. and T
A catalyst layer is formed by supporting a carrier such as iO2 or Alz 03.

Here, the supported amount of the catalyst component is preferably about 1 to 20%. When the loading rate is higher than this range, there is no commensurate improvement in nitrogen oxide removal efficiency, which is economically disadvantageous, and when the loading rate is lower than this range, there is no sufficient nitrogen oxide removal effect. I can't get it.

Examples of methods for supporting the catalyst component and carrier component include heating a wire mesh made of stainless steel to air oxidize the surface, and then supporting the catalyst thereon; A method for supporting a catalyst, a method for eluting a part of a steel wire to make it porous and supporting it on it, a method for oxidizing a metal plate coated with aluminum and a method for supporting a catalyst on it, electrophoresis of alumina on a metal plate. Examples include a method in which the catalyst component is supported by a catalyst and then a catalyst component is supported. Furthermore, methods such as converting the surface of a wire mesh or metal plate into a catalyst component by air oxidation, etc., or replacing a part of the constituent metals on the surface with other active metal abrasives electrochemically, etc. , is included in the support in the present invention.

The heating temperature of the catalyst component by the heating element is 200°C or higher, more preferably 250°C or higher when sulfur oxides coexist in the exhaust gas, and 150°C or higher when sulfur oxides do not coexist. , more preferably 200°C or higher.

Examples of reactors for carrying out the method of the present invention are shown in FIGS. 1 to 3. Figure 11 shows a cylindrical casing (1) in which a plurality of heating elements (2) carrying catalysts are arranged in parallel at regular intervals along the flow direction of exhaust gas (indicated by arrows). The exhaust gas is forced to pass perpendicularly to the plane of each heating element (2).

The reactor shown in FIG. 2 is similar to the reactor shown in FIG. 1, except that a corrugated heating element (2') is used to increase the efficiency of contact with the exhaust gas.

Figure 3 shows heating elements (3) arranged in parallel at regular intervals in a direction perpendicular to the flow direction of exhaust gas. be done.

In addition, the exhaust gas 1AIf sent to these reactors is 1AIf! If the temperature is low, nitrogen oxides and sulfur oxides in the exhaust gas may react with ammonia (2) and form salts before reaching the reactor.Therefore, to avoid this, ammonia injection should be done exothermically. body (2), (2°), (3)l, - preferably as close as possible.However, ammonia is uniformly distributed in the exhaust gas just before the heating element (2), (2°), (3). Care must be taken to ensure that they are mixed.

<Example> Next, the method of the present invention will be explained in detail by giving examples.

However, the present invention is not limited only to these examples.

Example 1 Ammonium metavanadate-ammonium metatungstate aqueous solution with an average particle size of 20μ and a specific surface area of 95
V2 using anatase-type titanium oxide with m'/g
A catalyst powder having a ratio of 0s:WO3:TiO2 of 4:10:86 (specific surface area: 88 m27 g, average particle size: 20 μm) was prepared. Next, 500 g of this catalyst powder and 100 g of 5i02 sol (Snowtex O, manufactured by Nissan Chemical ■) were thoroughly mixed to prepare a slurry having a slurry concentration of 1.00 g and 7M.

A 50-mesh nichrome wire mesh (4) shown in Fig. 4 (wire wire diameter 200μ, opening 300μ, cutting size 30μ x 35I1m) was immersed in this slurry, pulled up, and then ventilated with hot air at 50°C. Dry. moreover,
This was heat-treated at 200° C. for 18 hours to make it support.

Next, as shown in Figure 4, platinum electrodes (5) are attached to both sides of the 351 gourd of the nichrome wire mesh (4), and lead wires (6) are connected to these to connect the heating element (2). ) was obtained.

Seven pieces of this heating element (2) were installed in the reactor as shown in FIG. At this time, the dimensions of the reactor are the heating element (
2) The length from the first layer to the seventh layer is 701, and the gas contact area per catalyst volume (hereinafter referred to as Ap)
was 100 m'-J.

Example 2 Aluminum plated to a thickness of about 10μ
A 0μ 5US430 thin plate was lathed into 40 meshes. Using this, a corrugated molded body σ) as shown in FIG.
(carrier component) was produced.

On the other hand, using a methylamine aqueous solution of ammonium metavanadate-ammonium molybdate and the same anatase-type titanium oxide used in Example 1, V205:M
OO3: Catalyst powder with Ti02 ratio of 4:5:91 (
Specific surface area 91 rr? Ig, average particle size 20μ) was prepared. Next, 500 g of this powder and 100 g of Ti0z sol (manufactured by Sakai Chemical Industry Corporation, TiO2 content 20%) were thoroughly mixed to prepare a slurry having a sludge IJ concentration of 100 g/N.

The corrugated molded body (7) was immersed in this slurry, pulled up, and then dried with hot air at 50°C. Furthermore, this was heat-treated at 200° C. for 18 hours. Then,
In addition, as shown in FIG. 6, in the same manner as in Example 1,
Attach the platinum electrodes (5) and (5), and then connect the lead wire (6).
) and (6) were connected to obtain a heating element (8).

This heating element (8) was loaded into the reactor so that the gas flow was parallel to the surface of the heating element (8), as shown in FIG. The height of the corrugate at this time is 2.5
■The distance between the mountains is 4. , Oau+.

Further, the length of the corrugated molded body q) was 70 m5 in the gas flow direction and 301 I in the lateral direction, and the number of corrugated molded bodies used was 10. At this time, Ap was approximately 1200M4.

Example 3 γ with a specific surface area of 180 nt'/g and an average particle size of 15 μ
- Using a methylamine aqueous solution of alumina powder, ammonium metavanadate, and chromium nitrate v205: Cr
20s: Catalyst powder with A1203 ratio of 5:5:90 (
Specific surface area 150rr? /g, average particle size 15μ). Next, 500 g of this catalyst powder and 100 g of Al2O3 sol (manufactured by Nissan Chemical, Al2O3 content 10%)
Thoroughly mix the slurry with a concentration of 100g/j! A slurry was prepared.

Add 5US304 thin plate (thickness 500μ,
After dipping and pulling up the
It was ventilated and dried with warm air at 50°C. Furthermore, add this to 20
Heat treatment was performed at 0°C for 18 hours.

Electrodes were attached to both sides of this 35 g+m thin plate made of 5US304, and lead wires were further connected to these electrodes.

As shown in FIG. 3, six of the obtained heating elements (3) were arranged in parallel at 51 intervals in a reactor in parallel to the gas flow direction. The dimensions of the reactor at this time were 70 mm in length along the gas flow direction.

Additionally, Ap was 200 m'm.

Comparative Example To 2 kg of the same catalyst powder obtained in Example 1, old methyl cellulose (trade name manufactured by Shin-Etsu Chemical ■) and water were added.
After thorough kneading, the honeycomb molded body was extruded using an extrusion molding machine, and after ventilation drying, it was dried at 100 ° C. for 18 hours.
It was baked at 450°C for 3 hours. The obtained honeycomb body was then placed in a reactor, and the specific surface area of this honeycomb body was 78 m'/g. Also, Ap at this time is 990
It was rn'4.

Denitrification Activity Test Using each of the reactors obtained in Examples 1 to 3 and Comparative Example, a nitrogen oxide removal test was conducted using a test apparatus having a flow sheet shown in FIG.

In FIG. 8, (9) is the reactor obtained in the example or comparative example, and this reactor is filled with nitrogen gas (00).
, nitrogen oxide filled container (11), ammonia filled container (1)
2) and the oxygen-filled container (13) are connected as shown in the figure so that they can be supplied to the reactor (9) at a predetermined ratio, and at the same time, steam can be supplied from the steam generator (14). In Examples 1 to 3, the heating element in the reactor (9) was connected to an AC power source (15) through a lead wire to supply electricity and generate heat. Note that the honeycomb body of the comparative example did not generate heat. On the other hand, a part of the exhaust gas discharged from the reactor (9) is sent to the NO analyzer (16), and the amount of residual NO is measured.

The nitrogen oxide (No 2 ) removal rate is determined by the following formula from the respective No 9 degrees at the inlet and outlet of the reactor (9).

Population Concentration - Outlet Concentration Inlet Concentration The reaction was carried out under the following two conditions: clean gas conditions and dirty gas conditions containing sulfur dioxide SO2 gas.

(ωClean gas conditions (gas components) (concentration) NO200ppm NH3200ppm 02 2% N20 10% N2 Remaining area velocity: 10 m'm' time Inlet gas temperature = 100℃ Mountain) Dirty gas conditions (gas components) (a degrees ) No 200ppm NH32001) I) ITI SO2500ppm 02 2% N20 10% N2 Remaining area rate: iom'4・hour Population gas temperature = 150°C Here, areal velocity (AV) is the gas processing rate per gas contact area. It is shown by the following formula.

A V −S V / A p where Ap is the gas contact area per catalyst area (rn”4
), S V is the gas treatment rate (1/hour) per catalyst volume.

Under these test conditions, the nitrogen oxide removal efficiency was investigated by changing the catalyst temperature. The results are shown in Tables 2 and 3, respectively.

Life Test Example 1 and Comparative Example were subjected to a long-term running test for 1000 hours under the same clean gas conditions (gas temperature 100° C.) and with different catalyst temperatures.

Similarly, for Example 3 and Comparative Example, a long-term running test for 1000 hours was conducted under the same dirty gas conditions (gas temperature 150° C.) as described above and with different catalyst temperatures.

The test results are shown in Tables 4 and 5, respectively.

From these test results, it can be seen that the exhaust gas treatment method of the example has an excellent effect of removing nitrogen oxides by heating the catalyst, and moreover, this effect lasts for a long period of time.

<Effects of the Invention> As described above, in the present invention, by increasing the catalyst temperature, the reaction between nitrogen oxides and ammonia on the catalyst surface occurs quickly, so that the catalyst performance is reduced even for low-temperature exhaust gas. There is no formation of salts, so deterioration of the catalyst is prevented, and costs are lower than in the case where the gas temperature is raised.

[Brief explanation of drawings]

Figures 1 to 3 are schematic sectional views showing examples of reactors for carrying out the method of the present invention, Figure 4 is a plan view showing the heating element obtained in Example 1, and Figure 5 is a schematic cross-sectional view showing an example of a reactor for implementing the method of the present invention. A schematic perspective view showing the corrugated molded body obtained in Example 2, FIG. 6 is a schematic perspective view showing a heating element using the above corrugated molded body, and FIG.
FIG. 8 is a schematic perspective view of a reactor equipped with the heating element shown in FIG. 8, and FIG. (1)...Casing, (2). (2"). (8)...Heating element

Claims (1)

[Claims] 1. In an exhaust gas treatment method in which nitrogen oxides contained in exhaust gas are reductively decomposed with ammonia, the exhaust gas and ammonia are passed through a catalyst supported on a heating element and heated by the heat from the heating element, whereby nitrogen in the exhaust gas is removed. An exhaust gas treatment method characterized by reducing and decomposing oxides.